In 1851 the Louisiana physician Dr. Samuel Cartwright observed
a behavior evident in African African Americans but absent in
whites. They tended to run away from slave plantations. He attributed
this odd behavior to a disease peculiar to Negroes. He even gave
the affliction a name, "drapetomania."

Cartwright's "run-away" disease elicits derisive laughter today.
So too do all the other 19th and early 20th century exertions
to distinguish races by facial angle, skull size, cranial index,
length of shin bone and blood type. Our growing knowledge of the
genome and human evolutionary history help us understand why all
such efforts to locate the source of innate racial difference
were doomed: it doesn't exist. Most geneticists and anthropologists
who study human variation agree that humans just don't come bundled
into three or four separate groups according to skin color and
other physical traits.

Nonetheless, "discoveries" of racial difference resurface in the
press with predictable regularity. Often they spotlight differential
rates of diseases, or responses to a drug. Sometimes they zero
in on a genetics study.

That was the case recently with a report published in Science
magazine (Dec. 20, 2002). Noah Rosenberg, Marcus Feldman and others
analyzed the variation in 377 different DNA sequences from 1056
individuals from around the world. They found that 95% of the
DNA variation they studied is due to differences between individuals
within any continent. But they also found they could use the remaining
5% of the variation as genetic "footprints" indicating the continent
from which an individual's recent ancestors came.

Some were quick to interpret these results as evidence that old-fashioned
notions of the "races of man" have been correct all along. But
does it? What do these studies actually tell us? And why should
our interpretations matter?

Reports about such studies commonly fall prey to three confusions:
they conflate DNA markers of ancestry with markers of race. They
mistake the fact that some gene variants are more common in some
populations than others as signs of racial "difference" between
those populations. And they assume that disparities in group outcomes
can be attributed to inborn, or genetic, differences between races.

The idea of biological race assumes traits come packaged together,
even color-coded for our convenience, as anthropologist Jonathan
Marks jokes. In otherwords, if biological race were real, we'd
find that skin color or other "racial" markers would correlate
with a suite of other genetic traits. Knowing an individual's
"race" should enable us to predict his or her other genes and
traits.

But the DNA sequences studied by Rosenberg and his colleagues
are not genes. Known by geneticists as "microsatellite short tandem
repeats" (and more colloquially as "junk DNA"), they do not code
for proteins, but just sit there taking up space in our DNA. Mutations
in DNA sequences that don't code for anything are not affected
by natural and sexual selection. They are neither selected for
nor against but are simply passed down, generation to generation.
Comparing these accumulated mutation patterns can provide clues
to ancient population movements. But they have no effect on physical
traits such as skin color or hair form or blood type.

In other words, the study accomplished the same thing our eyes
do everyday. You can look at someone and stand a pretty good chance
of identifying the continent where that person's recent ancestors
lived, especially if you're gazing at someone whose family has
resided in the same place for several generations - as did all
the subjects of the study.

But what's that got to do with "race"? We all have ancestors from
elsewhere - and if we go back far enough, about 70,000 or so years
ago, all our ancestors can be traced back to Africa. But if our
idea of race assumes that different groups each share among themselves
a different suite of inborn traits, then we have to ask, "What
difference makes a difference?" Certainly not micro-satellite
short tandem repeats.

Still, there's no question that some gene forms show up more often
in some populations than others: alleles that code for blue eyes,
or the A, B, O blood groups, and of course, those alleles that
influence skin color . (We all have the same 30,000 or so genes.
But some genes come in different forms, or varieties, called alleles.)
But just because some members of a population might carry a specific
gene form, doesn't mean all members do. Only a small percentage
of Ashkenazi Jews carry the Tay-Sachs allele. When a couple I
know were screened upon their pregnancy, the non-Jewish partner
was found to be the Tay-Sachs carrier, not the Jewish one.

That's because most human variation falls within, not between
populations. About 85% of all genetic variation can, on average,
be found within any local population, be they Swedes, Kikuyu,
or Hmong. About 94% can be found within any continental population,
consistent with what the Rosenberg Science study found. In fact,
there are no characteristics, no traits, not even one gene that
turns up in all members of one so-called race yet is absent from
others.

Take sickle cell. Doctors were long taught that sickle cell anemia
was a genetic disease of Negroes, a marker of their race. Yet
sickle cell is found among peoples from central and western Africa,
but not southern Africa. It is also carried by Turks, Yemenis,
Indians, Greeks, and Sicilians. That's because sickle cell arose
several thousand years ago as a mutation in one of the genes that
codes for hemoglobin. The mutation soon spread to successive populations
along the trade routes where malaria was common. It turns out
that inheriting one sickle cell allele confers resistance to malaria
and thus provides a selective advantage in malarial regions (inheriting
sickle cell alleles from both parents causes sickle-cell disease).
In other words, sickle cell, like tandem repeats in the Science
study, is a marker not of skin color or race but ancestry, or
more precisely, having ancestors from where malaria was common.

Like sickle cell, most traits are influenced by separate genes
and inherited independently one from another. They are said to
be "non-concordant." Someone with brown hair might carry A, B
or O blood. Sub-Saharan Africans tend to have dark skin. But so
too do Dravidians from India, Aborigines from Australia, and Melanesians
from the South Pacific. Large numbers of West Africans are lactose
intolerant as are Japanese, but East Africans aren't. German and
Papua New Guinean populations have almost exactly the same frequencies
of A, B and O blood. At one point on the genome an individual
might share a gene form common in Africa, at another site East
Asia, and still another, Europe. Jared Diamond and others have
pointed out that for each trait we can classify people into "races"
by that trait, each giving us different and overlapping races
depending on the trait selected.

Indeed, the Rosenberg team found they could cluster the individuals
in their sample into several different statistically significant
groups, only one of which corresponded to five continents. They
also found that no matter which clustering scheme they used, individuals
could be placed in more than one group.

The reason for all this within-group variation is because unlike
most other species, modern humans, Homo sapiens sapiens, are young,
only about 150,000 years or so old, and we've always moved. As
humans migrated around the globe, populations bumped into each
other and shared their mates - and genes. Sometimes genes flowed
across great distances - through trade, war, slavery, piracy,
exile and migration. More often they flowed from village to village
to village. Human populations just haven't been isolated from
each other long enough to evolve into separate sub-species, or
races.

Ancestry is important in genetics and health care. I would like
to know if I were descended from a population at risk for sickle
cell, or the blood disease porphyria, or Tay Sachs. Oliver Sachs
has even written famously of an island of the colorblind. But
because of non-concordance, the geographic shape of populations
at genetic risk for a specific disease or adverse drug response
change amoeba-like depending upon the trait under study. These
populations do not map onto what we think of as race. To assume
they do is medically troublesome on several accounts.

First, doctors might be tempted to use race as a very unreliable
surrogate for an individual's own unique ancestry and patterns
of inheritance. And insofar as 94% of all genetic variants can
be found within any continent, assigning someone to a "racial"
continent of origin is too gross a scale to narrow down the range
of possibilities very much. (Some variants do correlate on a finer
scale with ethnic groups, and on a scale smaller yet with recent
family descent.)

But a belief in biological race also obscures the very salient
consequences of race as lived experience. Race may be a biological
myth, a social construction, but it nonetheless remains very real.
It can even have biological effects. African Americans have among
the highest rates of hypertension in the world. This was long
assumed to be genetic, a "marker" of their nature. But then it
was found that West Africans have among the world's lowest hypertension
rates. A focus on race as innate biology, as genetic difference,
would lead health professionals and policy makers to overlook
social factors that might contribute to African American hypertension
and heart disease, including the added stressor of living in a
racist society.

Race is terribly relevant to life outcomes. The likelihood that
toxic waste has been dumped in your neighborhood, your ability
to get a home loan, the quality of your kid's education, connections
to job opportunities, whether or not you're likely to be followed
in a department store or pulled over by police, are all influenced
by your race. Race does matter. Not race as genetics but race
as lived experience, what sociologists call "social" race. Social
race is an important variable for health researchers and epidemiologists.

The factors that lead to differential outcomes between races live
not in any "racial" genes but in our social institutions and practices.
It's easy to confuse the two. But doing so, like Dr. Cartwright's
drapetomania, displaces our attention from those discriminatory
practices to the "nature" of the victims. Blindness to the continuing
impact of racism can be just as harmful as believing that race
is biologically real. They both let society off the hook.

Larry Adelman is Series Executive Producer of RACE - The Power
of an Illusion and co-director of California Newsreel.